Z axis oscillating motion for routing marble and granite

If you are having trouble with a step in the commanded output caused by where in the wave pattern the signal from the sigen is connected or disconnected from the position command. perhaps you may need to run it through a limit2 component as well.
linuxcnc.org/docs/html/man/man9/limit2.9.html

So the hal arrangement might look something like this.

You could consider writing your own hal component. This would let you save the current position in a static variable so it can be referenced on the next pass through the servo loop.There are some included in the external offset branch but look at some of the simpler examples to understand how this works.
compiles and installs a component

hi
the oscillation of the tool is something common in alphacam stone
check in the you tube for example videos

Yes I found it out eventually in Alphacam, so I gave up on doing it trough Linuxcnc .

Thanks Yannis

You are in stone business ?

Not really, I was just retrofitting one Ravelli Teorema stone router, but I am glad if I can be of any help just ask